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Aircraft interception

Intercepting a Rockwell B-1B Lancer. Note the distance and angle to the intercepted aircraft. This position would be typical for the first phase of an interception.

Aircraft interception is when one aircraft moves up to another aircraft. Most often this relates to when a military aircraft is intercepting a civilian aircraft that is entering national airspace without a filed flight plan, entering restricted or prohibited airspace through misnavigation, aircraft having communication failures or aircraft that can not otherwise be identified. For those cases there is internationally standardised procedures.

Interception in FlightGear

Good manners

While in real life practice interception of civilian aircraft is not supposed to be done it can be a fun challenge in FlightGear. There is a few points to consider though:

Be polite, other pilots are more likely to be friendly if you are friendly.

Don't expect other pilots to have a clue about the procedures below, and accept that they may not be interested.

Do not fire upon, ram, redirect or stray into an intercepted aircraft. While it wont crash it is very annoying to its pilot.

At any time the intercepted aircraft may tick the "Ignore" box.

Challenges

Getting to know your aircraft

Getting to know your aircraft is part of the process to acquire skills used when intercepting aircraft. Military pilots have access to a flight manual that almost always include climb schedules and charts for optimum climb (usually for both fastest climb and fuel efficient climb), time to altitude, fuel to altitude and endurance for different mission profiles. By taking notes you might develop rules of thumb for those performance data.

Screenshots

Taking good screenshots of the interceptions is a bit fun, and can probably be more fun if you are two intercepting pilots.

Procedures for interception of civilian aircraft in real life

There is a set of standard procedures defined by ICAO that includes radio communication and visual signals both for night and day. There are procedures both for the intercepting aircraft and for the intercepted aircraft. These are defined in annex 2 to the convention on international civil aviation, Rules of the air, and are repeated in the Aeronautical information publication (AIP) for each country in section ENR 1.12, Interception of civilian aircraft. Note that there might be some national differences.

Intercepting aircraft

The intercepting aircraft should try to contact the intercepted aircraft using 121.5 MHz, using the call signs Interceptor <call sign>, Intercepted aircraft and Intercept control. If that fails the intercepting aircraft should try the ATC frequencies or try to contact the intercepted aircraft through the ATC.

Interception manoeuvres for visual identification is split into three phases.

Phase I: The intercepting aircraft moves up on the intercepted aircraft to about 300 metres distance from behind and slightly above. The flight leader or lone intercepting aircraft takes a position slightly ahead, above and normally to the left of the intercepted aircraft (or to the right if the intercepted aircraft is a helicopter) while maintaining a distance of about 300 metres.

Phase II: The flight leader or lone intercepting aircraft gently moves in close enough to identify the intercepted aircraft type and identity and get other information required, while the rest of the intercepting aircraft continues to stay well clear of the intercepted aircraft.

Phase III: The flight leader or lone intercepting aircraft gently brakes away from the intercepted aircraft in a shallow dive, while the rest of the intercepting aircraft continues to stay well clear of the intercepted aircraft till they can rejoin the flight leader.

If the intercepted aircraft have to be redirected the flight leader takes up a position ahead, above and normally to the left of the intercepted aircraft making sure that its pilot can see the intercepting aircraft.

Intercepted aircraft

When intercepted the pilot of the intercepted aircraft should:

Follow instruction given by intercepting aircraft, interpreting and responding to visual signals as mentioned below

Notify ATC if possible

Try establishing radio contact with intercepting aircraft or intercept control using 121.5 MHz or if that is not possible 243 MHz, stating the aircraft identity and the nature of the flight

Set the transponder to 7700 (emergency) unless instructed otherwise

If instructions from ATC and intercepting aircraft differs, the pilot of the intercepting aircraft should ask for clarification while continuing to follow instructions from the intercepting aircraft.

Visual signals

Initiated by intercepting aircraft

Series

Intercepting aircraft

Meaning

Intercepted aircraft

Meaning

1

Day or night. Rocking aircraft and flashing navigational lights at irregular intervals (landing lights for helicopters), from slightly ahead and above and normally to the left side of the intercepted aircraft (normally to the right side of intercepted helicopters).

After acknowledgement a slow level turn normally to the left (normally to the right of intercepted helicopters) to the desired heading.

Note 1: Terrain or weather may require series one manoeuvres to be done in the opposite direction.

Note 2: If the intercepted aircraft is unable to keep pace with the intercepted aircraft, the intercepting aircraft should do race track patterns around the intercepted aircraft, rocking the aircraft every pass.

You have been intercepted. Follow me.

Day or night. Rocking aircraft, flashing navigation lights at irregular intervals and following.

Day or night. An abrupt break away and climbing 90 degree turn or more not crossing the intercepted aircraft's path.

You may proceed.

Day or night. Rocking aircraft.

Understood. I will comply.

3

Day or night. Lowering landing gear (if possible), turning on the landing lights and overflying the runway in use. (Overflying the helicopter landing area if the intercepted aircraft is a heicopter, and coming to a hover near the landing area.

Land at this aerodrome.

Day or night. Lowering landing gear (if possible), turning on the landing lights and, after flying over the runway, landing if it is considered safe.

Understood. I will comply.

Initiated by intercepted aircraft

Series

Intercepted aircraft

Meaning

Intercepting aircraft

Meaning

4

Day or night. Raising landing gear, flashing the landing lights and passing over the runway in use at an altitude between 1 000 and 2 000 ft and continuously to circle the runway in use (if the intercepted aircraft is a helicopter flying over the landing area at an altitude between 170 ft and 330 ft and continuously circling the landing area).

If unable to flash landing lights flash any other lights available.

Aerodrome you have designated is inadequate.

Day or night. If it is desired to land the aircraft at an alternate aerodrome, the intercepting aircraft raises its landing gear and proceeds with series 1 signals for intercepting aircraft.

Understood. Follow me.

Day or night. If it is decided to release the intercepted aircraft, the intercepting aircraft raises its landing gear and proceeds with series 2 signals for intercepting aircraft.

Understood. You may proceed

5

Day or night. Regular switching on and off all available lights in a manner that is distinct from flashing lights.

I can not comply.

Day or night. The intercepting aircraft uses series 2 signals for intercepting aircraft.

Understood.

6

Day or night. Irregular flashing of all available lights.

I am in distress.

Day or night. The intercepting aircraft uses series 2 signals for intercepting aircraft.

Understood.

Reasons for interception in real life

Civilian aircraft

While interception of civilian aircraft is a last resort, interception is often the only means available to identify an aircraft that have not filed a flight plan and/or have no transponder and can not be contacted. Apart from identification interception is as well often the only means to redirect an aircraft that is straying into limited airspace or is believed to be involved in illegal activities.

Identification

Visual identification of aircraft that can not otherwise be identified.

Redirection

An aircraft may be intercepted and through visual signals or radio communication on emergency channels be requested to change route and possibly to land at an specific airport if an aircraft

is straying away from a route,

are entering a danger, restricted or prohibited area,

are suspected to fly illegally or is smuggling goods or persons,

enters a country's airspace without permit and fails to follow instructions to leave the airspace or land at a specific airport,

enters a country's airspace at different positions or routes than permitted, or

is a hazard to other aircraft

Military aircraft

There is of course also the case of military aircraft intercepting other military aircraft. During the Cold War many interceptions of intelligence, surveillance and spying aircraft from both the the western and eastern block where made. Interceptions where also sometimes made to redirect aircraft that actually tried to probe the opponents airspace. And of course there is interception to shoot down enemy aircraft.

Identification

Visual identification of aircraft that can not otherwise be identified. Sometimes done well outside of sovereign airspace or air defense identification zones (ADIZ's) to identify aircraft appearing in regular patterns and and with regular timing.

Redirection

Redirection of opponent aircraft trying to probe sovereign airspace to test air defenses.

Shooting down

Shooting down opponents aircraft trying to attack your territory.

Some background on interception and radars

On the multiplayer maps FlightGear anyone will see some information about an aircraft. Callsign, type of aircraft, altitude and speed are all readily available.

When an aircraft is not equipped with a transponder and have not filed a flight plan, air traffic control or an air force will only see an unidentified blip moving. The only way to identify it is to get an another aircraft close enough to do a visual identification.

In real life this is only the case if the aircraft both have filed a flight plan and are equipped with a transponder and there is both a primary radar, which bounces radio waves at the aircraft, a secondary radar, which interrogate the aircrafts transponder. Note that for civilian aircraft the transponder only will supply an four digit identity that the pilot have gotten from air traffic control and sometimes the altitude, which will be given in 100 feet intervals.

An older primary radar would basically only report the position of an aircraft and nothing else. Sometimes there would be a height finding radar co-located with the primary radar, but the height finding radar could only be used to find the altitude of one aircraft at a time. Newer primary radars will often report both the position and and approximate altitude.